The present invention relates broadly to an electromagnetic interference (EMI) shielding or grounding panel assembly including a porous, electrically-conductive shielding media and an electrically-conductive frame for supporting the media, and more particularly to such an assembly which is adapted to cover a corresponding ventilation opening in an electronics housing or other enclosure enclosures and which accommodates the flow of cooling air into the enclosure while maintaining electrical continuity and EMI shielding effectiveness across the opening.
The operation of electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. As is detailed in U.S. Pat. Nos. 5,202,536; 5,142,101; 5,105,056; 5,028,739; 4,952,448; and 4,857,668, such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed xe2x80x9celectromagnetic interferencexe2x80x9d or xe2x80x9cEMIxe2x80x9d as being known to interfere with the operation of other proximate electronic devices. xe2x80x9cEMIxe2x80x9d is used herein interchangeably with the term xe2x80x9cradio frequency interferencexe2x80x9d (xe2x80x9cRFIxe2x80x9d).
For attenuating EMI effects, shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other xe2x80x9ctargetxe2x80x9d devices from other source devices. Such shielding is provided as a barrier which is interposed between the source and the other devices, and most often is configured as an electrically conductive and grounded housing or other enclosure, such as a room, which surrounds the EMI generating circuitry of the source device. However, when such circuitry is contained within the confined space of an enclosure, it often is necessary to provide a cooling or ventilation means to dissipate the heat which is ohmicly or otherwise generated by the circuitry. Most enclosures therefore are formed with one or more air intake and/or exhaust openings or ports for natural or forced convective circulation of air between the interior of the enclosure and the ambient environment.
Left uncovered, such openings would represent a discontinuity in the surface and ground conductivity of the enclosure, with the result of a decrease in the EMI shielding effectiveness of the enclosure. Accordingly, shielded vent panels have been proposed for covering the openings in an manner which allows for the ventilation of the enclosure while electrical continuity, i.e., grounding, across the vent opening is maintained. In basic construction, such vent panels, which are sized to span the corresponding opening in the enclosure, conventionally are formed as including a sheet of a porous, electrically-conductive shielding media, and an electrically-conductive frame member configured to support the media as extending about the outer periphery thereof. The media, which may be an expanded metal mesh or, alternatively, a honeycombed-structured or other cellular structured metal foil, is received in or is otherwise attached to the frame, which typically is provided as an extruded aluminum or other metal profile. The frame, in turn, may be fastened to the enclosure over the opening thereof with screws or the like, with a compressible, electrically-conductive seal or gasket optionally provided for improved electrical contact between the frame and the enclosure.
However, for electrical continuity to be maintained across the opening, good electrical contact must be provided not only as between the frame and the enclosure, but also as between the media and the frame. In this regard, conventional panels may employ a C-shaped frame channel or other extrusion including a V-shaped or other projection or edge integrally formed within one of the sides of the channel. With the periphery of the media being received within the channel, the sides thereof are compressed to cause the projection or edge to penetrate into the media and thereby establish good electrical contact. Vent panels of such type are marketed commercially by the Chomerics Division of Parker-Hannifin Corp. (Woburn, Mass.) under the tradenames xe2x80x9cCho-Cell(trademark),xe2x80x9d xe2x80x9cShield Cell(copyright),xe2x80x9d xe2x80x9cOmni Cell(copyright),xe2x80x9d xe2x80x9cSlimvent(trademark),xe2x80x9d and Streamshield(trademark). Alternatively, the media may be fit into the frame and then bonded thereto using a conventional joining technique such as resistance welding, brazing, soldering, or the like. Vent panels of this type are marketed commercially by the Chomerics Division of Parker-Hannifin Corp. under the designation xe2x80x9csteel and brass honeycomb shielded vents.xe2x80x9d
EMI shielding vents also are described in commonly-assigned U.S. Pat. Nos. 6,426,459; 6,362,417; and 6,211,458; 5,032,689. Other vents and materials therefor are described in U.S. Pat. Nos. 3,546,359; 3,580,981; 3,553,343; 3,584,134; 3,821,463; 4,616,101; 4,249,033; 4,616,101; 5,007,946; 5,401,914; 5,895,885; and 5,910,639, JP 8064988, and WO 97/32459.
In view of the proliferation of electronic devices, it is to be expected that continued improvements in EMI shielded vent panels would be well-received by industry, and particularly by the designers of enclosures for personal computers, file servers, telecommunication equipment, and similar systems which now operate at frequencies of 500 MHz or more. Indeed, as the clock speeds of electronic devices continue to increase with the attendant generation of higher frequency EMI radiation and greater heat output, enclosure designers are faced with the seemingly competing requirements of providing both adequate ventilation and effective EMI shielding. In such applications, a honeycomb shielding media, such as is disclosed in U.S. Pat. Nos. 3,821,463; 5,895,885; 5,910,639, often may be considered preferred over other media as known to provide effective EMI shielding at higher frequencies with less restriction to air flow. Moreover, certain applications may specify a cast or similar-type frame construction which, in contrast to an extrusion, may be formed without corner seams and, as a result, may be made more structurally rigid and may be formed into more complex shapes. Ultimately, a preferred vent construction would be economical to manufacture, and would exhibit both reliable EMI shielding performance and good ventilation even in high frequency applications.
The present invention is directed to an EMI shielded vent construction including an electrically-conductive frame and an electrically-conductive, porous shielding media member, which is supported by the frame. The frame may be a casting and may be formed into a relatively rigid, relatively complex geometry such as being divided into one or more openings. Such frame is provided as a two or more piece arrangement including at least an top, upper, or other first frame member and a mating bottom, lower, or other second frame member which together define at least one opening for the media. Each of the frame members has an inside face which confronts the media, and an outside face. At least one of the frame members is formed as having a tooth, ridge, or other projection which depends from the inside face thereof as extending about at least a portion of the opening. With the media interposed between the inside faces of the frame members, such projection may be made to engage an overlapping portion of the media to thereby grip or otherwise positively retain the media between the frame members, and to provide electrical contact between the frame and the media. Advantageously, such retention and contact may be effected without the use of the solders or conductive adhesives which are conventionally employed to retain such media within frames of a casting or similar type.
The present invention, accordingly, comprises the EMI shielded vent panel possessing the combination of elements and construction as exemplified in the detailed disclosure to follow. Advantages of the present invention include a vent panel which exhibits reliable EMI shielding and air flow characteristics. Additional advantages include a panel construction which is economical and which allows for the use of a cast-type frame which may be formed without corner seams and, as a result, may be made more structurally rigid and may be formed into more complex shapes as compared to other frame types such as extrusions. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.